Multilayered ceramic capacitor, mounting structure of circuit board having thereon multilayered ceramic capacitor, packing unit for multilayered ceramic capacitor

ABSTRACT

There is provided a multilayered ceramic capacitor, including: a ceramic body; an active layer including a plurality of first and second internal electrodes; an upper cover layer; a lower cover layer formed below the active layer, the lower cover layer being thicker than the upper cover layer; first and second external electrodes; at least one pair of first and second internal electrodes repeatedly formed inside the lower cover layer, wherein, when A is defined as 1/2 of an overall thickness of the ceramic body, B is defined as a thickness of the lower cover layer, C is defined as 1/2 of an overall thickness of the active layer, and D is defined as a thickness of the upper cover layer, a ratio of deviation between a center of the active layer and a center of the ceramic body, (B+C)/A, satisfies 1.063≦(B+C)/A≦1.745.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 14/731,229 filed onJun. 4, 2015, which is a continuation of U.S. application Ser. No.13/764,193 filed on Feb. 11, 2013, now U.S. Pat. No. 9,087,646, whichclaims the priority of Korean Patent Application No. 10-2012-0126449filed on Nov. 9, 2012, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a multilayered ceramic capacitor, amounting structure of a circuit board having thereon the multilayeredceramic capacitor, a packing unit for the multilayered ceramiccapacitor.

Description of the Related Art

A multilayered ceramic capacitor, a multilayered chip electroniccomponent, is a chip-type condenser commonly mounted on the printedcircuit boards of various electronic products, such as image displaydevices including a liquid crystal display (LCD) and a plasma displaypanel (PDP), computers, personal digital assistants (PDAs), mobilephones, and the like, implementing charging and discharging ofelectricity therein.

Multilayered ceramic capacitors (MLCCs) may be used as components ofvarious electronic products due to a small size, high capacitance, andease of mountability.

A multilayered ceramic capacitor may have a structure in which aplurality of dielectric layers and a plurality of internal electrodeshaving different polarities and having the dielectric layers interposedtherebetween are alternately laminated with each other.

Since the plurality of dielectric layers have both piezoelectric andelectrostrictive properties, a piezoelectric phenomenon may occur,causing vibrations among the internal electrodes when AC or DC voltageis applied to the multilayered ceramic capacitor.

Such vibrations may be transferred through external electrodes of themultilayered ceramic capacitor to a printed circuit board on which themultilayered ceramic capacitor is mounted, and the entire printedcircuit board may become an acoustic reflection surface generating soundfrom the vibrations.

The sound generated by the vibrations may correspond to an audiblefrequency within the range of 20 to 20000 Hz, and this vibrating sound,frequently causing an unpleasant feeling in people is known as acousticnoise.

In order to reduce acoustic noise, products in which a lower cover layerof the multilayered ceramic capacitor is enlarged have been researched.

Generally, equivalent series inductance (ESL) is proportional to thearea of a current loop.

Therefore, as described above, the multilayered ceramic capacitor inwhich a lower cover layer is enlarged can partially reduce acousticnoise, but may have higher ESL as compared with products of the relatedart of which the lower cover layer is relatively thin.

The related art document below illustrates improvement in ESL, but failsto disclose a structure in which a lower cover layer includes aninternal electrode.

RELATED ART DOCUMENT

Korean Patent Laid-Open Publication No. 10-2006-0084770

SUMMARY OF THE INVENTION

An aspect of the present invention provides new measures capable ofreducing noise generated due to vibrations caused by a piezoelectricphenomenon in a multilayered ceramic capacitor and maintaining ESL at apredetermined level or lower.

According to an aspect of the present invention, there is provided amultilayered ceramic capacitor, including: a ceramic body having aplurality of dielectric layers laminated therein; an active layerincluding a plurality of first and second internal electrodes havingindividual dielectric layers interposed therebetween to formcapacitance, the first and second internal electrodes being alternatelyexposed through respective end surfaces of the ceramic body; an uppercover layer formed above the active layer; a lower cover layer formedbelow the active layer, the lower cover layer being thicker than theupper cover layer; first and second external electrodes covering bothend surfaces of the ceramic body; and at least one pair of first andsecond internal electrodes repeatedly formed inside the lower coverlayer with the dielectric layer interposed therebetween, the first andsecond internal electrodes being alternately exposed through both endsurfaces of the lower cover layer, wherein, when A is defined as 1/2 ofan overall thickness of the ceramic body, B is defined as a thickness ofthe lower cover layer, C is defined as 1/2 of an overall thickness ofthe active layer, and D is defined as a thickness of the upper coverlayer, a ratio of deviation between a center of the active layer and acenter of the ceramic body, (B+C)/A, satisfies 1.063≦(B+C)/A≦1.745.

Here, a ratio of the thickness (D) of the upper cover layer to thethickness (B) of the lower cover layer, D/B, may satisfy0.021≦D/B≦0.422.

Here, a ratio of the thickness (B) of the lower cover layer to 1/2 (A)of the overall thickness of the ceramic body, B/A, may satisfy0.329≦B/A≦1.522.

Here, a ratio of 1/2 (C) of the overall thickness of the active layer tothe thickness (B) of the lower cover layer, C/B, may satisfy0.146≦C/B≦2.458.

The first and second internal electrodes formed inside the lower coverlayer may be formed adjacently to a bottom surface of the ceramic body.

Here, when E is defined as an overall thickness of the first and secondinternal electrodes formed inside the lower cover layer, a ratio of theoverall thickness of the first and second internal electrodes formedinside the lower cover layer to the thickness of the lower cover layer,E/B, may be 0.5 or lower.

Here, when F is defined as a thickness from a lowermost edge of thefirst or second internal electrode formed inside the lower cover layerto a bottom surface of the ceramic body, F may be 100 μm or smaller.

Here, points of inflection formed on respective end surfaces of theceramic body may be formed to have a height corresponding to or lowerthan a center of the ceramic body in the thickness direction, due to adifference between a deformation rate occurring in the center of theactive layer and a deformation rate occurring in the lower cover layer,during the application of voltage thereto.

According to another aspect of the present invention, there is provideda mounting structure of a circuit board having a multilayered ceramiccapacitor mounted thereon, the mounting structure including: a printedcircuit board having first and second electrode pads formed thereon; anda multilayered ceramic capacitor mounted on the printed circuit board,wherein the multilayered ceramic capacitor includes: a ceramic bodyhaving a plurality of dielectric layers laminated therein; an activelayer including a plurality of first and second internal electrodeshaving the dielectric layer interposed therebetween, the first andsecond internal electrodes being alternately exposed through both endsurfaces of the ceramic body; an upper cover layer formed above theactive layer; a lower cover layer formed below the active layer, thelower cover layer being thicker than the upper cover layer and having atleast one pair of first and second internal electrodes alternatelyexposed through both end surfaces thereof; and first and second externalelectrodes formed on both end surfaces of the ceramic body to beelectrically connected to exposed portions of the first and secondinternal electrodes and soldering-connected to first and secondelectrode pads; and wherein, when A is defined as 1/2 of an overallthickness of the ceramic body, B is defined as a thickness of the lowercover layer, C is defined as 1/2 of an overall thickness of the activelayer, and D is defined as a thickness of the upper cover layer, a ratioof deviation between a center of the active layer and a center of theceramic body, (B+C)/A, satisfies 1.063≦(B+C)/A≦1.745.

Here, points of inflection formed on respective end surfaces of theceramic body may be formed to have a height corresponding to or lowerthan soldering, due to a difference between a deformation rate occurringin the center of the active layer and a deformation rate occurring inthe lower cover layer, during the application of voltage thereto.

According to another aspect of the present invention, there is provideda packing unit for a multilayered ceramic capacitor, the packing unitincluding: one or more multilayered ceramic capacitors, the one or moremultilayered ceramic capacitors including: a ceramic body having aplurality of dielectric layers laminated therein; an active layerincluding a plurality of first and second internal electrodes having thedielectric layer interposed therebetween, the first and second internalelectrodes being alternately exposed through both end surfaces of theceramic body; an upper cover layer formed above the active layer; alower cover layer formed below the active layer, the lower cover layerbeing thicker than the upper cover layer and having at least one pair offirst and second internal electrodes alternately exposed through bothend surfaces thereof; and first and second external electrodes formed onboth end surfaces of the ceramic body and electrically connected toexposed portions of the first and second internal electrodes, whereinwhen A is defined as 1/2 of an overall thickness of the ceramic body, Bis defined as a thickness of the lower cover layer, C is defined as 1/2of an overall thickness of the active layer, and D is defined as athickness of the upper cover layer, a ratio of deviation between acenter of the active layer and a center of the ceramic body, (B+C)/A,satisfies 1.063≦(B+C)/A≦1.745; and a packing sheet having a plurality ofreceiving parts in which the multilayered ceramic capacitors arerespectively received, the lower cover layer of the multilayered ceramiccapacitor facing a bottom surface of the receiving part.

The packing unit may further include a packing film attached to onesurface of the packing sheet so as to seal the receiving parts in whichthe multilayered ceramic capacitors are respectively received.

The packing sheet may be wound as a reel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a partially cutaway perspective view schematically showing amultilayered ceramic capacitor according to an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view showing the multilayered ceramiccapacitor of FIG. 1, cut in the length direction thereof;

FIG. 3 is a cross-sectional view schematically showing the multilayeredceramic capacitor of FIG. 1, cut in the length direction thereof, toillustrate dimensional relationships among components included in themultilayered ceramic capacitor;

FIG. 4 is a partially cutaway perspective view showing a state in whichthe multilayered ceramic capacitor of FIG. 1 is mounted on a printedcircuit board;

FIG. 5 is a cross-sectional view showing the multilayered ceramiccapacitor and printed circuit board of FIG. 4, cut in the lengthdirection thereof;

FIG. 6 is a cross-sectional view schematically showing a state in whichthe multilayered ceramic capacitor of FIG. 4 is transformed due to theapplication of voltage when the multilayered ceramic capacitor ismounted on the printed circuit board;

FIG. 7 is a perspective view schematically showing a state in which themultilayered ceramic capacitor according to the embodiment of thepresent invention is mounted on a packing unit;

FIG. 8 is a cross-sectional view schematically showing a state in whichthe packing unit of FIG. 7 is wound as a reel;

FIG. 9 is a graph showing an impedance change to frequency for amultilayered ceramic capacitor of the related art, a multilayeredceramic capacitor having a lower cover layer, and a multilayered ceramiccapacitor having a lower cover layer of the present embodiment in whichfirst and second internal electrodes are further formed; and

FIG. 10 is a graph showing an ESL change to frequency for a multilayeredceramic capacitor of the related art, a multilayered ceramic capacitorhaving a lower cover layer, and a multilayered ceramic capacitor havinga lower cover layer of the present embodiment in which first and secondinternal electrodes are further formed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The invention may,however, be embodied in many different forms and should not be construedas being limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art.

In the drawings, the shapes and dimensions of elements may beexaggerated for clarity, and the same reference numerals will be usedthroughout to designate the same or like elements.

When directions of a hexahedron are defined in order to clearly describeembodiments of the present invention, L, W, and T directions, shown inthe drawings, indicate length, width, and thickness directions,respectively. Here, the thickness direction may be used to have the sameconcept as a lamination direction in which dielectric layers arelaminated.

In addition, in the present embodiments, end surfaces of a ceramic bodyin a length direction thereof, on which first and second externalelectrodes are formed, are defined as both end surfaces, and surfacesperpendicular to the end surfaces are defined as side surfaces.

Multilayered Ceramic Capacitor

Referring to FIGS. 1 and 2, a multilayered ceramic capacitor 100according to an embodiment of the present invention may include aceramic body 110, an active layer 115 having first and second internalelectrodes 121 and 122, upper and lower cover layers 112 and 113, andfirst and second external electrodes 131 and 132 formed to cover bothend surfaces of the ceramic body 110. At least one pair of first andsecond internal electrodes may be formed inside the lower cover layer113.

The ceramic body 110 may be formed by laminating and firing a pluralityof dielectric layers 111. The shapes, dimensions, and the number ofstacked dielectric layers 111, of the ceramic body 110 are not limitedto those described in the present embodiment.

The plurality of dielectric layers 111 constituting the ceramic body 110are in a sintered state, and boundaries between adjacent dielectriclayers 111 may be integrated such that they may not be readily apparentwithout the use of a scanning electron microscope (SEM).

The ceramic body 110 may be composed of the active layer 115contributing to capacitance formation and the upper cover layer 112 andthe lower cover layer 113 as margin parts, formed above and below theactive layer 115.

The active layer 115 may be formed by repeatedly laminating a pluralityof first and second internal electrodes 121 and 122 with the dielectriclayer 111 between the first internal electrode and the second internalelectrode.

Here, the thickness of the dielectric layer 111 may be optionallychanged according to the design of capacitance of the multilayeredceramic capacitor 100, and the thickness of one layer may be 0.01 to1.00 μm after firing, but the present invention is not limited thereto.

In addition, the dielectric layer 111 may contain ceramic powder havinga high dielectric constant, for example, barium titanate (BaTiO₃) basedpowder or strontium titanate (SrTiO₃) based powder, but the presentinvention is not limited thereto.

The upper cover layer 112 and the lower cover layer 113 may have thesame material and constitution as the dielectric layer 111, except thatthe internal electrodes are not included therein.

The upper cover layer 112 and the lower cover layer 113 may be formed bylaminating a single dielectric layer or two or more dielectric layers onupper and lower surfaces of the active layer 115 in upper and lowerdirections, respectively. The upper cover layer 112 and the lower coverlayer 113 may basically serve to prevent damage of the first and secondinternal electrodes 121 and 122 due to physical or chemical stress.

In addition, the lower cover layer 113 may be thicker than the uppercover layer 112 by further increasing the number of laminated dielectriclayers as compared with the upper cover layer 112.

Here, since equivalent series inductance (ESL) is proportional to thearea of a current loop, the lower cover layer 113 of the multilayeredceramic capacitor may be enlarged to thereby reduce vibrations of theinternal electrodes and thus reduce acoustic noise, but in that case,ESL may be increased.

However, in the present embodiment, acoustic noise may be reduced andESL may be maintained at a predetermined level or lower by forming atleast one pair of first and second internal electrodes 123 and 124inside the lower cover layer 113.

This effect of preventing ESL reduction may further be improved when thefirst and second internal electrodes 123 and 124 formed inside the lowercover layer 113 are formed more adjacently to a lower end of the lowercover layer 113.

The first and second internal electrodes 121 and 122 are a pair ofelectrodes having different polarities, and may be formed by printingconductive paste containing conductive metal at a predeterminedthickness on the dielectric layers 111 such that the first and secondinternal electrodes 121 and 122 are alternately exposed through both endsurfaces of the ceramic body in a lamination direction in which thedielectric layers 111 are stacked. The first and second internalelectrodes 121 and 122 may be electrically insulated from each other bythe dielectric layers 111 disposed therebetween.

That is, the first and second internal electrodes 121 and 122 may beelectrically connected to the first and second external electrodes 131and 132 through portions thereof alternately exposed through both endsurfaces of the ceramic body 110.

Therefore, when voltages are applied to the first and second externalelectrodes 131 and 132, charges are stored between the first and secondinternal electrodes 121 and 122 facing each other. Here, the capacitanceof the multilayered ceramic capacitor 100 may be proportional to thearea of an overlapping region of the first and second internalelectrodes 121 and 122.

The thickness of each of the first and second internal electrodes 121and 122 may be determined depending on the usage thereof, and forexample, may be determined within a range of 0.2 to 1.0 μm inconsideration of the size of the ceramic body 110. However, the presentinvention is not limited thereto.

In addition, conductive metal contained in the conductive paste forforming the first and second internal electrodes 121 and 122 may benickel (Ni), copper (Cu), palladium (Pd), or an alloy thereof, but thepresent invention is not limited thereto.

In addition, the conductive paste may be printed by a screen printingmethod, a gravure printing method, or the like, but the presentinvention is not limited thereto.

The first and second external electrodes 131 and 132 may be formed of aconductive paste containing a conductive metal. The conductive metal maybe nickel (Ni), copper (Cu), palladium (Pd), gold (Au), or an alloythereof, but the present invention is not limited thereto.

Hereinafter, the relationship between dimensions of components includedin the multilayered ceramic capacitor according to the presentembodiment and acoustic noise will be described.

Referring to FIG. 3, A is defined as 1/2 of an overall thickness of theceramic body 110, B is defined as a thickness of the lower cover layer113, C is defined as 1/2 of an overall thickness of the active layer115, D is defined as a thickness of the upper cover layer 112, E isdefined as an overall thickness of the first and second internalelectrodes 123 and 124 formed inside the lower cover layer 113, and F isdefined as a thickness of a part of the lower cover layer 113 in whichthe first and second internal electrodes 123 and 124 are not formed.

Here, the overall thickness of the ceramic body 110 refers to a distancebetween the top surface (S_(T)) and the bottom surface (S_(B)) of theceramic body 110. The overall thickness of the active layer 115 refersto a distance between an upper surface of the first internal electrode121 located at the uppermost portion of the active layer 115 to a lowersurface of the second internal electrode 122 located at the lowermostportion of the active layer 115.

In addition, the thickness of the lower cover layer 113 (B) refers to adistance between a lower surface of the second internal electrode 122located at the lowermost portion in the thickness direction of theactive layer 115 to the bottom surface (S_(B)) of the ceramic body 110,and the thickness of the upper cover layer 112 (D) refers to a distancebetween an upper surface of the first internal electrode 121 located atthe uppermost portion in the thickness direction of the active layer 115to the top surface (S_(T)) of the ceramic body 110.

When voltages having different polarities are applied to the first andsecond external electrodes 131 and 132 formed on both ends of themultilayered ceramic capacitor 100, the ceramic body 110 expands andshrinks in the thickness direction thereof due to an inversepiezoelectric effect of the dielectric layers 111, and both ends of thefirst and second external electrodes 131 and 132 expand and shrink,contrary to the expansion and shrinkage of the ceramic body 110 in thethickness direction of the ceramic body 110, due to the Poisson effect.

Here, a center of the active layer 115 may correspond to portions of thefirst and second external electrodes 131 and 132 corresponding to bothends of the multilayered ceramic capacitor in the length directionthereof in which significant expansion and shrinkage occur, whichbecomes a factor causing acoustic noise.

That is, in the present embodiment, in order to reduce acoustic noise,points of inflection (PI) formed on respective end surfaces of theceramic body 110 may be formed to have a height corresponding to orlower than a center (CL_(C)) of the thickness of the ceramic body 110,due to a difference between a deformation rate occurring in the center(CL_(A)) of the active layer 115 and a deformation rate occurring in thelower cover layer 113, during the application of voltage thereto.

Here, in order to further reduce acoustic noise, a ratio of deviationbetween the center (CL_(A)) of the active layer 115 and the center(CL_(C)) of the ceramic body 110, (B+C)/A, may satisfy1.063≦(B+C)/A≦1.745.

In addition, the ratio of the thickness (D) of the upper cover layer 112to the thickness (B) of the lower cover layer 113, D/B, may satisfy0.021≦D/B≦0.422.

In addition, the ratio of the thickness (B) of the lower cover layer 113to 1/2 (A) of the thickness of the ceramic body 110, B/A, may satisfy0.329≦B/A≦1.522.

In addition, the ratio of 1/2 (C) of the thickness of the active layer115 to the thickness (B) of the lower cover layer 113, C/B, may satisfy0.146≦C/B≦2.458.

Experimental Example

Multilayered ceramic capacitors according to the inventive examples andcomparative examples of the present invention were manufactured asfollows.

A slurry including a powder of, for example, barium titanate (BaTiO₃) orthe like, was coated and dried on carrier films, to prepare a pluralityof ceramic green sheets having a thickness of 1.8 μm.

Then, a conductive paste for a nickel internal electrode was coated onthe ceramic green sheets by using a screen, to form internal electrodes.

The ceramic green sheets were laminated in an amount of about 370 layerswhile ceramic green sheets not having internal electrodes formedthereon, rather than the ceramic green sheets having internal electrodesformed thereon, were laminated in greater numbers in a lower part of thelaminate than in an upper part thereof. This laminate was subjected toisostatic pressing at 85° C. in the pressure conditions of 1000 kgf/cm².

The ceramic laminate after completion of pressing was cut intoindividual chips, and then the cut chip was subjected to debindering at230° C. in the air atmosphere for 60 hours.

After that, the resultant chip was fired in the reducing atmosphereunder an oxygen partial pressure of 10⁻¹¹ atm to 10⁻¹² atm, lower thanthe equilibrium oxygen partial pressure of Ni/NiO, such that theinternal electrodes are not oxidized, at 1200° C. The chip size of amultilayered chip capacitor after firing was about 1.64 mm×0.88 mm (L×W,1608 size). Here, the tolerance was within a range of ±0.1 mm inlength×width (L×W), and when the range is satisfied, acoustic noise wasmeasured by experimentation.

Then, an external electrode forming process, a plating process, and thelike were carried out to manufacture multilayered ceramic capacitors.

TABLE 1 Capacitance A B C D AN Implementation Sample (μm) (μm) (μm) (μm)(B + C)/A B/A D/B C/B (dB) Ratio  1* 405.5 40.2 365.4 39.9 1.000 0.0990.993 9.090 29.5 OK  2* 436.0 70.4 365.9 69.7 1.001 0.161 0.990 5.19725.7 OK  3* 455.5 90.8 364.3 91.5 0.999 0.199 1.008 4.012 23.1 OK  4*508.1 24.9 361.1 269.1 0.760 0.049 10.807 14.502 31.2 OK  5* 456.6 25.2360.1 167.8 0.844 0.055 6.659 14.290 32.5 OK  6* 527.3 30.2 191.0 642.40.419 0.057 21.272 6.325 30.3 OK  7* 414.5 30.9 188.8 420.4 0.530 0.07513.605 6.110 30.5 OK  8* 516.2 39.4 360.7 271.5 0.775 0.076 6.891 9.15528.2 OK  9* 446.0 39.8 365.5 121.2 0.909 0.089 3.045 9.183 29.1 OK  10*469.1 40.6 364.2 169.1 0.863 0.087 4.165 8.970 27.9 OK  11* 416.2 40.7360.7 70.3 0.964 0.098 1.727 8.862 28.4 OK  12* 428.3 40.8 360.0 95.70.936 0.095 2.346 8.824 28.9 OK  13* 495.9 40.9 364.9 221.0 0.818 0.0825.403 8.922 28.1 OK  14* 435.9 25.0 421.3 4.2 1.024 0.057 0.168 16.85231.6 OK  15* 420.7 70.4 365.9 39.1 1.037 0.167 0.555 5.197 25.7 OK 16431.7 94.8 364.3 40.0 1.063 0.220 0.422 3.843 19.9 OK 17 443.0 103.8389.1 4.0 1.113 0.234 0.039 3.749 19.3 OK 18 443.7 119.8 363.2 41.11.089 0.270 0.343 3.032 18.7 OK 19 447.1 147.3 362.1 22.7 1.139 0.3290.154 2.458 17.9 OK 20 452.8 164.7 360.2 20.4 1.159 0.364 0.124 2.18717.3 OK 21 448.7 170.3 361.0 5.1 1.184 0.380 0.030 2.120 17.2 OK 22470.7 170.4 365.4 40.2 1.138 0.362 0.236 2.144 17.4 OK 23 491.9 220.3360.8 41.8 1.181 0.448 0.190 1.638 16.9 OK 24 500.6 270.2 360.5 9.91.260 0.540 0.037 1.334 16.8 OK 25 516.9 270.4 361.8 39.7 1.223 0.5230.147 1.338 16.7 OK 26 502.1 364.9 312.3 14.7 1.349 0.727 0.040 0.85616.6 OK 27 407.5 421.8 189.1 14.9 1.499 1.035 0.035 0.448 16.6 OK 28445.8 493.3 179.3 39.7 1.509 1.107 0.080 0.363 16.5 OK 29 483.7 632.0160.1 15.2 1.638 1.307 0.024 0.253 16.4 OK 30 520.0 643.4 190.7 15.21.604 1.237 0.024 0.296 16.4 OK 31 486.4 685.3 121.1 45.3 1.658 1.4090.066 0.177 16.4 OK 32 507.2 742.7 120.8 30.1 1.702 1.464 0.041 0.16316.4 OK 33 515.2 773.9 118.2 20.1 1.732 1.502 0.026 0.153 16.4 OK 34524.5 798.2 116.9 16.9 1.745 1.522 0.021 0.146 16.3 OK  35* 533.4 832.4109.8 14.8 1.766 1.561 0.018 0.132 16.3 NG  36* 533.3 841.1 105.3 14.91.775 1.577 0.018 0.125 16.3 NG  37* 534.1 849.7 101.2 16.1 1.780 1.5910.019 0.119 16.3 NG *Comparative Example, AN: acoustic noise

Table 1 above shows dimension data of respective parts of themultilayered ceramic capacitor 100, measured based on an image obtainedby scanning a cross-section of the ceramic body 110, cut in the lengthdirection (L) and the thickness direction (T) in the central portion ofthe ceramic body 110 of the multilayered ceramic capacitor 100 in thewidth (W) direction thereof, using a scanning electron microscope (SEM),as shown in FIG. 3.

Here, as described above, A was defined as 1/2 of an overall thicknessof the ceramic body 110, B was defined as a thickness of the lower coverlayer 113, C was defined as 1/2 of an overall thickness of the activelayer 115, and D was defined as a thickness of the upper cover layer112.

In order to measure acoustic noise, one sample (multilayered chipcapacitor) per a substrate for measuring acoustic noise was mounted on aprinted circuit board while upper and lower directions of the samplewere differentiated from each other, and then the printed circuit boardwas seated on a measuring jig.

In addition, DC voltage and voltage variations were applied to bothterminals of the sample seated on the measuring jig by using a DC powersupply and a function generator. Acoustic noise was measured through amicrophone installed directly above the printed circuit board.

In Table 1 above, Samples 1 to 3 are comparative examples having asymmetrical cover structure in which the thickness (B) of the lowercover layer 113 is approximately similar to the thickness (D) of theupper cover layer 112, and Samples 4 to 13 are comparative exampleshaving a structure in which the thickness (D) of the upper cover layer112 is thicker than the thickness (B) of the lower cover layer 113.

In addition, Samples 14, 15, and 35 to 37 are comparative exampleshaving a structure in which the thickness (B) of the lower cover layer113 is thicker than the thickness (D) of the upper cover layer 112, andSamples 16 to 34 are inventive examples according to the embodiment ofthe invention.

Here, in the case in which the (B+C)/A value is approximately 1, thecenter of the active layer 115 does not largely deviate from the centerof the ceramic body 110. In Samples 1 to 3 having a symmetrical coverstructure in which the thickness (B) of the lower cover layer 113 isapproximately similar to the thickness (D) of the upper cover layer 112,the (B+C)/A values thereof are approximately 1.

In the case in which the (B+C)/A value is greater than 1, the center ofthe active layer 115 upwardly deviates from the center of the ceramicbody 110. When the (B+C)/A value is smaller than 1, the center of theactive layer 115 downwardly deviates from the center of the ceramic body110.

Referring to Table 1 above, in Samples 16 to 34 in which the ratio ofdeviation between the center of the active layer 115 from the center ofthe ceramic body 110, (B+C)/A, satisfies 1.063≦(B+C)/A≦1.745, it can beconfirmed that acoustic noise values thereof were significantly reducedto below 20 dB.

In addition, Samples 1 to 15 in which the ratio of deviation between thecenter of the active layer 115 and the center of the ceramic body 110,(B+C)/A, is below 1.063, has a structure in which the center of theactive layer 115 scarcely deviates from the center of the ceramic body110 or the center of the active layer 115 downwardly deviates from thecenter of the ceramic body 110.

In the forgoing samples 1 to 15 of which the (B+C)/A value is below1.063, acoustic noise values thereof were 25 to 32.5 dB, and thus it canbe confirmed that the samples 1 to 15 had no effect of reducing acousticnoise as compared with the inventive examples according to theembodiment of the present invention.

In addition, in Samples 35 to 37 in which the ratio of deviation betweenthe center of the active layer 115 and the center of the ceramic body110, (B+C)/A, is above 1.745, the capacitance in comparison with thetarget capacitance was low, causing defective capacitance.

In Table 1 above, in the case that “NG” is marked in the column“Capacitance Implementation Ratio” (that is, the ratio of capacitance totarget capacitance), the value of capacitance to target capacitance isbelow 80% when the target capacitance value is 100%.

In addition, in the inventive examples in which the ratio of thethickness (D) of the upper cover layer 112 to the thickness (B) of thelower cover layer 113, D/B, satisfies 0.021≦D/B≦0.422, it can beconfirmed that acoustic noise was significantly reduced.

Whereas, in the comparative examples in which the ratio of the thickness(D) of the upper cover layer 112 to the thickness (B) of the lower coverlayer 113, D/B, is above 0.422, it can be confirmed that there was noeffect in reducing acoustic noise.

When the ratio of the thickness (D) of the upper cover layer 112 to thethickness (B) of the lower cover layer 113, D/B, is below 0.021, thethickness (B) of the lower cover layer 113 is excessively greater thanthe thickness (D) of the upper cover layer 112, resulting in cracking ordelamination, and the capacitance in comparison with target capacitanceis low, causing defective capacitance.

In Samples 19 to 34 of the inventive examples in which the ratio of thethickness (B) of the lower cover layer 113 to the thickness (A) of theceramic body 110, B/A, and the ratio of the thickness (C) of the activelayer 115 to the thickness (B) of the lower cover layer 113, C/B,satisfy, 0.329≦B/A≦1.522 and 0.146≦C/B≦2.458, it can be confirmed thatacoustic noise values therefor were further decreased to below 18 dB.

Whereas, in Samples 35 to 37 in which the ratio of the thickness (B) ofthe lower cover layer 113 to the thickness (A) of the ceramic body 110,B/A, is above 1.522 or the ratio of the thickness (C) of the activelayer 115 to the thickness (B) of the lower cover layer 113, C/B, isbelow 0.146, it can be confirmed that capacitance, in comparison withtarget capacitance, was low, causing defective capacitance.

Table 2 below shows changes of ESL (here, frequency: 200 MHz) andacoustic noise (dB) according to the thickness of the lower cover layer113 and the overall thickness of the first and second internalelectrodes 123 and 124 formed inside the lower cover layer 113.

TABLE 2 Thickness Thickness Thickness Thickness Thickness ThicknessAcoustic (A) (B) (C) (D) (E) (F) ESL Noise Sample (μm) (μm) (μm) (μm)(μm) (μm) E/B (pH) (dB) 1 510.0 251.2 364.8 40.1 150.1 40.4 0.598 14920.1 2 509.7 250.0 365.2 39.8 100.2 40.0 0.401 149 17.1 3 510.2 249.7365.9 40.5 71.8 40.3 0.288 151 16.9 4 508.5 250.8 364.3 40.8 41.1 40.10.164 150 16.8 5 509.8 249.2 364.2 40.4 21.4 40.2 0.086 148 16.7 6 510.1249.8 364.0 40.1 21.0 72.1 0.084 161 16.8 7 509.5 249.9 364.2 40.5 20.8100.0 0.083 169 16.9 8 510.4 251.0 364.8 40.2 20.9 149.5 0.083 211 16.89 510.2 250.1 364.5 40.1 0.0 — 0 320 16.8

In Table 2 above, (E) represents overall thickness of the first andsecond internal electrodes 123 and 124 formed inside the lower coverlayer 113, and (F) represents thickness from the second internalelectrodes 124 at the lowermost location to the bottom surface (SB) ofthe ceramic body 110.

Referring to Table 2, it can be confirmed that ESL exceeded 200 pH, inSample 9 as an example of the related art in which the first and secondinternal electrodes 123 and 124 are not formed inside the lower coverlayer 113, and in Sample 8 in which thickness (F) is above 100 μm.

In addition, it can be confirmed that acoustic noise exceeded 20 dB inSample 1 in which the ratio of thickness of the first and the secondinternal electrodes 123 and 124 to the overall thickness of the lowercover layer 113, E/B, is above 0.5.

Therefore, it can be seen that (F) and (E/B) were 100 μm or less and 0.5or smaller, respectively, in order to maintain ESL and acoustic noise ata predetermined level or lower.

FIG. 9 is a graph showing an impedance change to frequency for amultilayered ceramic capacitor of the related art (hereinafter,“Comparative Example 1”), a multilayered ceramic capacitor having alower cover layer (hereinafter, “Comparative Example 2”), and amultilayered ceramic capacitor having a lower cover layer in which firstand second internal electrodes are further formed (hereinafter,“Inventive Example”).

Referring to FIG. 9, Comparative Examples 1 and 2 had approximatelysimilar impedance values at low frequencies, but the impedance ofComparative Example 2 was increased relatively more than the impedanceof Comparative Example 1 and Inventive Example when the frequencyexceeded a predetermined value. It can be seen that, here, the impedanceof Inventive Example was nearly similar to the impedance of ComparativeExample 1 in which the lower cover layer 113 is not formed.

FIG. 10 is a graph showing an ESL change to frequency for ComparativeExamples 1 and 2 and Inventive Example.

Referring to FIG. 10, it can be seen that ESL of Inventive Example washigher than that of Comparative Example 1 and approximately similar tothat of Comparative Example 2 at relatively low frequencies, but wassignificantly lowered when the frequency exceeded a predetermined level,and thus remarkably lower than that of Comparative Example 2 andapproximately similar to that of Comparative Example 1 in which thelower cover layer 113 is not formed.

Therefore, the multilayered ceramic capacitor 100 according to thepresent embodiment may lower ESL to a level similar to that of theproduct of the related art in which the lower cover layer 113 is notformed while having a structure of reducing acoustic noise.

Mounting Structure of Circuit Board Having Multilayered CeramicCapacitor Mounted Thereon

Referring to FIGS. 4 and 5, a mounting board 200 for the multilayeredceramic capacitor 100 according to the present embodiment may include aprinted circuit board 210 on which the multilayered ceramic capacitor100 is horizontally mounted; and first and second electrode pads 221 and222 spaced apart from each other on an upper surface of the printedcircuit board 210.

Here, the multilayered ceramic capacitor 100 may be electricallyconnected to the printed circuit board 210 by soldering 230 while thelower cover layer 113 is located below and the first and second externalelectrodes 131 and 132 are positioned on and contacted with the firstand second electrode pads 221 and 222, respectively.

When voltage is applied while the multilayered ceramic capacitor 100 ismounted on the printed circuit board 210 as described above, acousticnoise may be generated.

Here, the size of the first and second electrode pads 221 and 222 may bean index for determining the amount of soldering 230 which connects thefirst and second external electrodes 131 and 132 of the multilayeredceramic capacitor 100 and the first and second electrode pads 221 and222, and the level of acoustic noise may be controlled depending on theamount of soldering 230.

Referring to FIG. 6, when voltages having different polarities areapplied to the first and second external electrodes 131 and 132 formedon both ends of the multilayered ceramic capacitor 100 while themultilayered ceramic capacitor 100 is mounted on the printed circuitboard 210, the ceramic body 110 expands and shrinks in the thicknessdirection thereof due to an inverse piezoelectric effect of thedielectric layers 111, and both ends of the first and second externalelectrodes 131 and 132 expand and shrink, contrary to the expansion andshrinkage of the ceramic body 110 in the thickness direction, due to thePoisson effect.

Here, a center of the active layer 115 corresponds to portions of thefirst and second external electrodes 131 and 132 corresponding to bothends of the multilayered ceramic capacitor in the length directionthereof in which significant expansion and shrinkage occur, and thisbecomes a factor causing acoustic noise.

When both end surfaces in the length direction of the multilayeredceramic capacitor 100 significantly expands, a force ({circle around(1)}) of allowing an upper portion of the soldering 230 to be pushed outto the outside is generated due to expansion and a shrinkage force({circle around (2)}) of allowing a lower portion of the soldering 230to be pushed to the external electrode is generated due to the force({circle around (1)}).

Therefore, when points of inflection formed on respective end surfacesof the ceramic body 110 is formed to have a height corresponding to orlower than the soldering 230 due to a difference between a deformationrate occurring in a center of the active layer 115 (CL_(A)) and adeformation rate occurring in the lower cover layer 113, during theapplication of voltage thereto, acoustic noise may be further reduced.

Packing Unit for Multilayered Ceramic Capacitor

Referring to FIG. 7, a packing unit 300 for a multilayered chipcapacitor according to the present embodiment may include a packingsheet 310 having a plurality of receiving parts 311 formed to correspondto multilayered ceramic capacitors 100 so as to receive the multilayeredceramic capacitors 100 therein, respectively.

Here, the respective multilayered ceramic capacitors 100 are maintainedby an electronic product arranging apparatus 420 such that the first andsecond internal electrodes 121 and 122 are horizontally arranged, andmay be conveyed to the packing sheet 310 by using a conveying apparatus410.

The thus conveyed multilayered ceramic capacitors 100 may be received inthe receiving parts 311 such that respective lower cover layers 113 ofthe multilayered ceramic capacitors 100 face a bottom surface 311 a ofthe receiving part 311.

In addition, a packing film 320 may be attached to one surface of thepacking sheet 310 so as to seal the receiving parts 311 in which themultilayered ceramic capacitors 100 are respectively received.

Meanwhile, referring to FIG. 8, the thusly formed packing sheet 310 maybe continuously wound as a reel.

As set forth above, according to the embodiments of the invention,vibrations generated from the multilayered ceramic capacitor may bedecreased and thus acoustic noise generated from the printed circuitboard may be reduced, and ESL may be maintained at a predetermined levelor lower.

While the present invention has been shown and described in connectionwith the embodiments, it will be apparent to those skilled in the artthat modifications and variations can be made without departing from thespirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A multilayered ceramic capacitor, comprising: aceramic body having an active layer including a plurality of first andsecond internal electrodes, an upper cover layer disposed above theactive layer, and a lower cover layer disposed below the active layerand including at least one pair of third and fourth internal electrodes,the third and fourth internal electrodes being alternately exposedthrough opposite end surfaces of the lower cover layer, respectively; afirst external electrode connecting the first and third internalelectrodes; and a second external electrode connecting the second andfourth internal electrodes, wherein the lower cover layer is thickerthan the upper cover layer, and a gap between the bottom of the activelayer and an uppermost internal electrode disposed inside the lowercover layer is greater than a gap between adjacent internal electrodesdisposed inside the active layer.
 2. The multilayered ceramic capacitorof claim 1, wherein, when A is defined as 1/2 of an overall thickness ofthe ceramic body, B is defined as a thickness of the lower cover layer,and C is defined as 1/2 of an overall thickness of the active layer, aratio of deviation between a center of the active layer and a center ofthe ceramic body, (B+C)/A, satisfies 1.063≦(B+C)/A≦1.745.
 3. Themultilayered ceramic capacitor of claim 2, when D is defined as athickness of the upper cover layer, wherein a ratio of the thickness (D)of the upper cover layer to the thickness (B) of the lower cover layer,D/B, satisfies 0.021≦D/B≦0.422.
 4. The multilayered ceramic capacitor ofclaim 2, wherein a ratio of the thickness (B) of the lower cover layerto 1/2 (A) of the overall thickness of the ceramic body, B/A, satisfies0.329≦B/A≦1.522.
 5. The multilayered ceramic capacitor of claim 2,wherein a ratio of 1/2 (C) of the overall thickness of the active layerto the thickness (B) of the lower cover layer, C/B, satisfies0.146≦C/B≦2.458.
 6. The multilayered ceramic capacitor of claim 2,wherein when E is defined as an overall thickness of the first andsecond internal electrodes disposed inside the lower cover layer, aratio of the overall thickness (E) of the first and second internalelectrodes disposed inside the lower cover layer to the thickness (B) ofthe lower cover layer, E/B, is 0.5 or lower.
 7. The multilayered ceramiccapacitor of claim 2, wherein when E is defined as an overall thicknessof the first and second internal electrodes disposed inside the lowercover layer and F is defined as a thickness from a lowermost internalelectrode disposed inside the lower cover layer to a bottom surface ofthe ceramic body, a ratio of the overall thickness of the first andsecond internal electrodes disposed inside the lower cover layer to theoverall thickness of the lower cover layer, E/B, is 0.5 or lower, and Fis 100 μm or smaller.
 8. The multilayered ceramic capacitor of claim 1,wherein a gap between the bottom surface of the ceramic body and thelowermost internal electrode disposed inside the lower cover layer isless than the gap between the bottom of the active layer and theuppermost internal electrode disposed inside the lower cover layer. 9.The multilayered ceramic capacitor of claim 1, wherein when F is definedas a thickness from a lowermost internal electrode disposed inside thelower cover layer to a bottom surface of the ceramic body, F is 100 μmor smaller.
 10. The multilayered ceramic capacitor of claim 1, whereinpoints of inflection formed on respective end surfaces of the ceramicbody are formed to have a height corresponding to or lower than a centerof the ceramic body in the thickness direction, due to a differencebetween a deformation rate occurring in the center of the active layerand a deformation rate occurring in the lower cover layer, during theapplication of voltage thereto.
 11. A mounting structure of a circuitboard having a multilayered ceramic capacitor mounted thereon, themounting structure comprising: a printed circuit board having first andsecond electrode pads formed thereon; and a multilayered ceramiccapacitor mounted on the printed circuit board, the multilayered ceramiccapacitor including: a ceramic body having an active layer including aplurality of first and second internal electrodes, an upper cover layerdisposed above the active layer, and a lower cover layer disposed belowthe active layer and including at least one pair of third and fourthinternal electrodes, the third and fourth internal electrodes beingalternately exposed through opposite end surfaces of the lower coverlayer, a first external electrode connecting the first and thirdinternal electrodes and solder-connecting the first electrode pad, and asecond external electrode connecting the second and fourth internalelectrodes and solder-connecting the second electrode pad, wherein thelower cover layer is thicker than the upper cover layer, and a gapbetween the bottom of the active layer and an uppermost internalelectrode disposed inside the lower cover layer is greater than a gapbetween adjacent internal electrodes disposed inside the active layer.12. The mounting structure of claim 11, wherein, when A is defined as1/2 of an overall thickness of the ceramic body, B is defined as athickness of the lower cover layer, and C is defined as 1/2 of anoverall thickness of the active layer, a ratio of deviation between acenter of the active layer and a center of the ceramic body, (B+C)/A,satisfies 1.063≦(B+C)/A≦1.745.
 13. The mounting structure of claim 11,wherein points of inflection formed on respective end surfaces of theceramic body are formed to have a height corresponding to or lower thansolder, due to a difference between a deformation rate occurring in thecenter of the active layer and a deformation rate occurring in the lowercover layer, during the application of voltage thereto.
 14. A packingunit for a multilayered ceramic capacitor, the packing unit comprising:one or more multilayered ceramic capacitors, the one or moremultilayered ceramic capacitors including: a ceramic body having anactive layer including a plurality of first and second internalelectrodes, an upper cover layer disposed above the active layer, and alower cover layer disposed below the active layer and including at leastone pair of third and fourth internal electrodes, the third and fourthinternal electrodes being alternately exposed through opposite endsurfaces of the lower cover layer, a first external electrode connectingthe first and third internal electrodes, and a second external electrodeconnecting the second and fourth internal electrodes, wherein the lowercover layer is thicker than the upper cover layer, and a gap between thebottom of the active layer and an uppermost internal electrode disposedinside the lower cover layer is greater than a gap between adjacentinternal electrodes disposed inside the active layer; and a packingsheet having a plurality of receiving parts in which the multilayeredceramic capacitors are respectively received, the lower cover layer ofthe multilayered ceramic capacitor facing a bottom surface of thereceiving part.
 15. The packing unit of claim 14, wherein, when A isdefined as 1/2 of an overall thickness of the ceramic body, B is definedas a thickness of the lower cover layer, and C is defined as 1/2 of anoverall thickness of the active layer, a ratio of deviation between acenter of the active layer and a center of the ceramic body, (B+C)/A,satisfies 1.063≦(B+C)/A≦1.745
 16. The packing unit of claim 14, furthercomprising a packing film attached to one surface of the packing sheetso as to seal the receiving parts in which the multilayered ceramiccapacitors are respectively received.
 17. The packing unit of claim 14,wherein the packing sheet is wound as a reel.
 18. A multilayered ceramiccapacitor, comprising: a ceramic body having an upper cover layer, alower cover layer having a thickness greater than that of the uppercover layer and including at least one pair of third and fourth internalelectrodes alternately disposed, and an active layer interposed betweenthe upper cover layer and the lower cover layer and including aplurality of first and second internal electrodes alternativelydisposed; a first external electrode disposed on the ceramic body andelectrically connecting the first and third internal electrodes; and asecond external electrode disposed on the ceramic body and electricallyconnecting the second and fourth internal electrodes, wherein a gapbetween one of the first and second internal electrodes and one of thethird and fourth internal electrodes is greater than a gap between anyother two immediately adjacent internal electrodes, the one of the firstand second internal electrodes and the one of the third and fourthinternal electrodes being two immediately adjacent internal electrodes.19. The multilayered ceramic capacitor of claim 18, wherein the one ofthe first and second internal electrodes and the one of the third andfourth internal electrodes are not located at the center of the ceramicbody.
 20. The multilayered ceramic capacitor of claim 18, wherein, whenA is defined as 1/2 of an overall thickness of the ceramic body, B isdefined as a thickness of the lower cover layer, and C is defined as 1/2of an overall thickness of the active layer, a ratio of deviationbetween a center of the active layer and a center of the ceramic body,(B+C)/A, satisfies 1.063≦(B+C)/A≦0.745.
 21. The multilayered ceramiccapacitor of claim 20, when D is defined as a thickness of the uppercover layer, wherein a ratio of the thickness (D) of the upper coverlayer to the thickness (B) of the lower cover layer, D/B, satisfies0.021≦D/B≦0.422.
 22. The multilayered ceramic capacitor of claim 20,wherein a ratio of the thickness (B) of the lower cover layer to 1/2 (A)of the overall thickness of the ceramic body, B/A, satisfies0.329≦B/A≦1.522.
 23. The multilayered ceramic capacitor of claim 20,wherein a ratio of 1/2 (C) of the overall thickness of the active layerto the thickness (B) of the lower cover layer, C/B, satisfies0.146≦C/B≦2.458.
 24. The multilayered ceramic capacitor of claim 20,wherein when E is defined as an overall thickness of the first andsecond internal electrodes disposed inside the lower cover layer, aratio of the overall thickness (E) of the first and second internalelectrodes disposed inside the lower cover layer to the thickness (B) ofthe lower cover layer, E/B, is 0.5 or lower.
 25. The multilayeredceramic capacitor of claim 20, wherein when E is defined as an overallthickness of the first and second internal electrodes disposed insidethe lower cover layer and F is defined as a thickness from a lowermostinternal electrode disposed inside the lower cover layer to a bottomsurface of the ceramic body, a ratio of the overall thickness of thefirst and second internal electrodes disposed inside the lower coverlayer to the overall thickness of the lower cover layer, E/B, is 0.5 orlower, and F is 100 μm or smaller.
 26. The multilayered ceramiccapacitor of claim 18, wherein when F is defined as a thickness from alowermost internal electrode disposed inside the lower cover layer to abottom surface of the ceramic body, F is 100 μm or smaller.
 27. Themultilayered ceramic capacitor of claim 18, wherein points of inflectionformed on respective end surfaces of the ceramic body are formed to havea height corresponding to or lower than a center of the ceramic body inthe thickness direction, due to a difference between a deformation rateoccurring in the center of the active layer and a deformation rateoccurring in the lower cover layer, during the application of voltagethereto.